Latex particles obtained by emulsion polymerization can have a variety of applications, including for use as model colloids for calibration of instruments used to measure particle size, for immobilization of biomolecules (such as proteins or peptides) on the surface of the particles, for development of new types of immunoassays, and for film formation for ink-jet printing, painting, and coating applications. While latex particulates have applications in these and other fields, the ink-jet ink imaging application can be used to favorably illustrate unique advantages of latexes. Specifically, there has been great improvement in the area of water durability of ink-jet inks through incorporation of certain ink-jet compatible latex polymers. When printed as part of an ink-jet ink, a latex component of the ink can form a film on a media surface, entrapping and protecting the colorant within the hydrophobic print film.
While latex particulates can improve durability of prints, they often exhibit undesirable qualities while in suspension. Water-soluble polymers can increase the viscosity of a suspension because of dissolution. When the suspension is an ink, the viscosity can affect printability. Particularly, higher viscosity inks often do not print properly. Further, if it is possible to print the ink, the water-soluble polymers can remain the same once printed, thus reducing the overall printed image durability. To overcome these drawbacks, water insoluble latex particulates can be added to a suspension. The addition of more water insoluble latex particulates typically only increase the viscosity of a suspension, e.g. ink, only slightly compared to the addition of water soluble polymers, and are therefore more desirable. Insoluble latex particulates have drawbacks, though. They tend to settle out of and/or agglomerate in suspensions over time and, therefore, often are not stable in many storage conditions.
Latex particulates can be prepared through conventional emulsion polymerization processes. In this method, hydrophobic monomers are emulsified in water. Free-radical initiators are often used to initiate the polymerization. In some systems, dispersants can be added to the latex dispersion in an attempt to improve dispersion and stability of the latex particulates; however, such solutions leave something to be desired. This being the case, there is a continuing need to provide latex particulates that provide improved stability and printability.